Theravāda Vinayapiṭaka
Monks’ rules and their analysis
Monks’ Training (Sekhiya) 52
… in Anāthapiṇḍika’s monastery. Now at that time the group of six monks ate licking the fingers …
‘I will not eat licking the fingers,’ is a training to be observed.”
One should not eat licking the fingers … if he is the first wrong-doer.